Usage of solar collectors is becoming more and more widespread in view of the energy problems which are slowly becoming known. Solar collectors are particularly suited for the house technique for heating up of water to be used and for heating up of water for warm-water heating systems. However, the thermal yield, in relationship to the unit area of a solar collector, is not very great, in particular in regions in which there is not much sunshine. However, particularly in these moderate and colder regions much heat energy is used up. In order to replace an amount of the energy consumption, which amount is worth mentioning, with solar energy, solar collectors must have relatively large surface areas, for example several square meters for a one-family house. The building costs of heat-producing systems with solar collectors are considerable. Even though operating expenses are hardly created, the profitableness of such systems is still low because of the high capital investment. For a better profitableness, it is important to manufacture solar collectors as inexpensively as possible.
Various forms of solar collectors are known, for example those which have a dark-colored pipeline system, through which a liquid is moved. The liquid is heated up by the radiant heat energy of the sun and a reflection is substantially avoided by the dark coloring. The mentioned glazing prevents the heat which is absorbed by the collector from being radiated back.
A pipeline system can be manufactured particularly inexpensively with the aid of a blow molded absorber plate. The manufacture of a pipeline system from a blow-molded part is known from German OS No. 24 44 706 for a flat-heating element and can in principle also be utilized in a solar collector.
To achieve a further reduction in price during the manufacture of solar collectors, the basic purpose of the invention is to design a solar collector, in which the pipeline system is formed by a blow-molded absorber plate so that aside from the blow-molded absorber plate, the glazing and possibly heat-insulation material, no further parts are needed for the actual solar collector.
This purpose is attained according to the invention in such a manner that a hollow frame which is made of one piece with the blow-molded absorber plate is formed on the edge of the plate-shaped blow-molded absorber plate, which frame has a closed cross section.
Such a collector is extremely inexpensive, because the support construction, in which the pipeline system is arranged, consists of one piece with this pipeline system and is manufactured during the same operation. It is only still possible to mount on the blow-molded absorber plate a glazing and possibly on the back side thereof heat insulation material. Further operations are not needed. Because of the inexpensive manufacturing possibility, it is possible to provide also large surface areas at an affordable price. With the aid of the invention because of a strong reduction of the building costs, the feasability of heat-producing systems utilizing solar collectors is improved considerably. The hollow frame which is formed on the edge of the blow-molded absorber plate has a sufficient stability to hold a relatively large collector surface, for example a collector surface of approximately 1 m.sup.2, reliably in its mold.
Grooves are preferably provided in the frame. As a result, the glazing plate and/or an insulation layer can be mounted and held comfortably in their correct position, without requiring special aligning operations. The glazing which is permeable for the heat radiation is spaced as a rule a certain distance from the pipes of the pipeline system to define an air space therebetween, for which reason a fluted mortise has a suitable position relative to the pipes. The insulation layer, however, can rest directly on the pipes or it may have also a certain spacing therefrom. Fluted mortises are not absolutely necessary, because a glazing or an insulation layer, for example could rest on the upper side or the bottom side of the frame.
The arrangement of support projections has the advantage that the solar collector has as a whole a greater rigidity. Also this prevents large-surface glazings from sagging in the midsection. The arrangement of the support projections will be chosen in accordance with the respective size, form and remaining structure of the collector. The collector may have any desired basic forms. In most cases one will choose a basic rectangular form. However, the invention is not limited to this. To adjust to special surface relationships, it is also possible for other forms to be advantageous.
Fastening holes are mounted preferably on the corners of the frame. However, this is also not absolutely necessary. It would also be possible to hold a collector for example also with clamps or other fastening elements, which do not extend through the blow-molded absorber plate, but only grip around same.
The pipeline system may be designed differently. For example a zigzag channel 7 is preferable.
A particularly preferable manufacture of a solar collector can be achieved, as stated above, by the blow-molding process. The communication between the cavities during the manufacturing process has the advantage that blown air needs to be supplied at only one single point. However, it is also easily possible to provide several supply points. The cavities then do not need to communicate with one another, if to every connected cavity an air supply is connected.
The form of the frame results in a particularly good rigid structure crosswise of the frame plane. Since solar collectors are generally arranged lying inclined to the vertical, for example on a roof surface, rigidity in this direction is particularly advantageous. Also a thin frame takes up little surface so that the surface which is utilized for the production of heat is not reduced too much by the frame.
The inventive solar collector has also the advantage that it is particularly lightweight. This again has an effect on the entire building costs of a heat-producing system because the solar collector applies only a small load to a support structure, for example the roof construction of a house, and this roof construction can be constructed correspondingly with a smaller load factor.
As a material, plastics of any kind which can be worked in the blow-molding process can be used if they are sufficiently resistant to the deteriorating effects of the sun's radiation. Black-colored polypropylene is well suited.